This invention relates to a three-phase motor having a stator winding connected to a three-phase input by a multiple speed stator winding construction.
Electric motors are often required for operating at two different speeds. Various systems have been provided for controlling the speed of the motor including the use of alternate windings, one for each speed. A single phase motor is disclosed in U.S. Pat. No. 3,359,476 in which a plurality of windings are provided in a multiple section arrangement. All of the windings used are one speed while only a part of the windings are employed but in a different connection, to provide an alternate and different speed. The dual functioning winding, however, provides a more efficient use of the winding space than motors having completely separate windings for different speeds. The system is restricted to a single phase motor. Further, a special motor starting switch arrangement is used for the motor winding connections and the system limits the starting of the motor to a single speed arrangement, with switch over means when the second speed is desired. Further, many larger motors employ a three-phase winding configuration for connection to a three-phase power supply. The prior art has employed various series-parallel winding combinations to control the power output ratio of the two speed winding arrangements. They, however, produced relatively large steps in changes in power ratios. A much smaller or finer change in steps can be provided in the system of the above patent which permits appropriate selection of a conductor slot for controlling the magnetic effects of the turns in the motor coils in one speed when compared to the other alternate speed. The multiple section winding is thus desirable because it allows the designer to more accurately distribute the turns in the slots which are most effective in each speed connection. However, the prior art systems have been limited to the various separate windings, complex series-parallel combinations and the like.